Criminal – Assault and battery on person 60 years old

Where (1) a jury was not instructed to specify on the jury slip the theory of liability on which they rested their verdict, (2) the jury returned a general verdict finding the defendant guilty of assault and battery by means of a dangerous weapon on a person 60 years old and (3) the evidence was sufficient to support a conviction on a joint venture theory but not on a principal liability theory, the conviction must be reversed.